1. Field of the Invention
This invention relates to dust disposal cyclones and more particularly to cyclones of the recycling type.
As is known, there are--for ecological reasons--very strict limits as to the amounts of dust which may be exhausted into the ambient atmosphere.
2. Description of the Prior Art
For the removal of dust from air various apparatus have been employed. One of them is the cyclone in which dust is removed by means of the centrifugal force generated in the dust laden air introduced tangentially into the cyclone. Dust particles are impelled towards the wall of the cyclone along which they descend while the air freed of dust ascends and withdraws through the clean air outlet of the cyclone. Such cyclones are distinguished by their low costs, simple structure and reliable operation since they have no moving component parts. However, the collection efficiency of such simple cyclones generally does not meet the requirements imposed by ecological considerations because finer dust particles will still be exhausted into the atmosphere with the withdrawn air.
In order to improve dust removal by means of cyclones it is known to connect two or more cyclones in series. It has, however, been found that the collection efficiency of the second cyclone of the series connection is considerably lower than that of the cyclone upstream thereof which is due to a materially lower dust load of the air introduced into the downstream cyclones of the series. In addition, the resistances of the cyclones to the airflow therethrough are additive which is undesirable for economy of energy.
Therefore, it has been suggested to use the clean air outlet of a cyclone as a second stage. The dust deposited on the wall of the clean air outlet is recycled from the clean air outlet into the dust collecting chamber of the cyclone. Thus, a double stage dust collection is obtained in a single cyclone as is the case with the recycling Typ MGXU of the firm Gebruder Buhler AG Maschinenfabrik, Uzwill, Switzerland.